*{
    box-sizing: border-box;
}
body{
    background-color: #eafbff;
    /* 背景渐变 */
    background-image:linear-gradient(
        to bottom, 
        #eafbff 0%,
        #eafbff 50%,
        #5290f9 50%,
        #5290f9 100%
    );
    display: flex;
    align-items: center;
    justify-content: center;
    height: 100vh;
    margin: 0;
}
nav{
    background-color: #fff;
    padding: 70px;
    width: 80px;
    display: flex;
    align-items: center;
    justify-content: center;
    border-radius: 3px;
    box-shadow: 0 2px 5px rgba(0, 0, 0, 0.3);
    transition: width 0.6s linear;
    overflow-x: hidden;
}
.active{
    width: 450px;
}
nav ul{
    display: flex;
    list-style-type: none;
    padding: 0;
    margin: 0;
    width: 0;
    transition: width 0.6s linear;
}
.active ul{
    width: 100%;
}
nav ul li{
    transform:rotateY(0deg);
    opacity:0;
    transition:transform 0.6s linear,opacity 0.6s linear;
}
.active ul li{
    opacity: 1;
    transform: rotateY('360deg');
}
nav ul a{
    position: relative;
    color:black;
    text-decoration: none;
    margin: 0 10px;
}
.icon{
    background-color: #fff;
    border:0;
    cursor: pointer;
    padding: 0;
    position: relative;
    width: 30px;
    height: 30px;
}
.icon .line{
    background-color: #5290f9;
    height: 2px;
    width: 20px;
    position: absolute;
    top:10px;
    left: 5px;
    transition: transform 0.6s linear;
}
.icon .line2{
    top:auto;
    bottom: 10px;
}
.active .icon .line1{
    transform: rotate(-765deg) translateY(5.5px);
}
.active .icon .line2{
    transform: rotate(765deg) translateY(-5.5px);
}